The international attention drew more than a million viewers to Olivia's song and helped raise $77,000 for the Liv Wise Fund that was started in her name in support of brain tumor research.

The video shows OIivia sitting in a wheelchair in the middle of the studio, singing softly at first and struggling with her breaths.

"'Cause I am a champion, and you're gonna hear me roar."

Her energy grows and she smiles as she sings "I got the eye of a tiger, a fighter, dancing through the fire."

"Olivia is a fighter and has gone through the fire," her cousin wrote in the post under the video posting on YouTube. "In fact, she was going through the fire while she recorded this song, but you wouldn't know it, because she was dancing right through it."

Her family posted another song video on YouTube just days before Olivia's death. She wrote "Simple Girl" -- a song about how she wanted to live life -- when she was 11. The only time she sang it was on September 6, during the same session in which she recorded "Roar."

"In many ways, Olivia has lived a shortened, but full life," her mother wrote in the letter to CNN.

Wise was diagnosed with a very aggressive form of brain cancer in January 2012 after she suffered a seizure.

She rarely complained about the grave prognosis, her mother said. "Every day, she wished for a cure, and rarely succumbed to negative thoughts."

"To tell the truth, her diagnosis didn't change her personality," her mom said. "It only enhanced it. She took the news in a mature, reasonable, responsible way. ... Even in the most difficult moments, she managed to bring laughter and friendship to all that were caring for her."